Pyrithione salts, such as zinc pyrithione, are known to provide excellent antimicrobial activity, including broad spectrum anti-bacterial and anti-fungal activity. Pyrithiones have been widely used in various applications, for example, metal working fluids, paints and personal care compositions such as shampoos. Pyrithiones also have utility in urethane applications, such as shoe inserts and beddings.
Unfortunately, some of the useful pyrithione salts are solids, and the use of solids, such as powders, in the formulating and processing of polyurethanes is undesirable for environmental and safety concerns since the handling of a powder is generally a dusty process. Moreover, it has been difficult to effectively incorporate solid pyrithione salts such as pyrithione powders directly into polyurethanes since it is hard to evenly disperse these salts in polyurethanes.
Efforts have been made in the past to introduce pyrithione salts into polyurethanes. By way of illustration, U.S. Pat. No. 5,114,984 discloses a process for producing an antimicrobially effective polyurethane which includes the steps of dissolving a pyrithione salt(s) in an alkanolamine to provide a dissolved pyrithione salt, incorporating the dissolved pyrithione salt into a polyol to provide a liquid mixture and reacting the liquid mixture with a polyisocyanate to produce a polyurethane having antimicrobial activity. However, alkanolamines are catalytically active components in polyurethane reactions. Therefore, the pyrithione salt alkanolamine solution can't be added to the existing polyurethane formulae directly without adjusting these formulae beforehand. This causes inconvenience and is generally undesirable in commercial settings. Further, the solution of pyrithione salts in alkanolamines may be of very high viscosity. Sometimes, paste-like substances are formed because of strong hydrogen bonding arising between polar alkanolamines and pyrithione salts, which makes the pyrithione salt alkanolamine solution difficult to handle.
Another approach to incorporate pyrithione salts into polyurethanes is by including an aqueous dispersion of pyrithione salts in the polyurethane forming composition. Compared with solid pyrithione salts, aqueous pyrithione salt dispersion is easier to handle. However, water is a foaming agent in flex foam formulations and is unacceptable in many non-foam applications such as coatings, elastomers and sealants. Accordingly, formula adjustment is needed before an aqueous pyrithione salt dispersion can be added to any flex foam and non-foam formulations. In addition, the polyurethane foams produced in the presence of aqueous dispersion of pyrithione salts tend to have closed cell structures. It is known that foams having closed cells have low air flow property. Such foams normally feel uncomfortable and undesirable in many situations.
U.S. Pat. No. 6,294,589 discloses a process to incorporate a partially encapsulated antimicrobial agent such as zinc pyrithione into polyurethanes. The process includes the steps of at least partially encapsulating an antimicrobial agent with a plasticizer material and dispersing the encapsulated antimicrobial agent into at least one of either the components used to fabricate the polyurethane or the mixture into which the components are combined to create the polyurethane. However, the additional step of encapsulating the antimicrobial agent adds cost to the production of polyurethane and may not be desirable.
As such, it is appreciated that there is still a need for an easy and cost efficient method that effectively disperse pyrithione salts uniformly throughout the polyurethanes.